A conventional rotation angle detecting device as disclosed in a patent document 1 comprises a primary rotation body to rotate as integral with a rotation body and two of secondary rotation bodies to rotate as coupled with such the primary rotation body. Moreover, the primary rotation body and two of the secondary rotation bodies individually comprises a gear, wherein the number of teeth of the individual gears are different from each other. Further, each of the gears of the individual secondary rotation bodies and the gear of the primary rotation body are meshed with each other respectively. Furthermore, each of the secondary rotation bodies individually comprises a magnet and an anisotropic magnetoresistive (AMR) sensor to detect a magnetic field of the individual magnets. And then it calculates a rotation angle of the rotation body, by using such as a phase difference between each of detection signals for the rotation angles of the individual secondary rotation bodies that each of the AMR sensors outputs.
On the contrary, a conventional rotation angle detecting device as disclosed in a patent document 2 comprises a rotating plate to be rotated using a rotation body and a gear to be rotated with the number of rotation as larger than that of the rotating plate by using the rotation body or the rotating plate. Moreover, there is provided an encoder of absolute signal type at the rotating plate, and then a code signal is output as a rotation angle detection signal for the rotating plate, which is determined as one cycle for one rotation of the rotating plate by such the encoder. Further, there is provided a magnetic sensor that a magnet and a magnetoresistive element are used therefor at the gear, and then an analog signal is output as a rotation angle detection signal for the gear, which is determined as one cycle for one rotation of the gear by such the magnetic sensor. Furthermore, a rotation angle of the rotation body is calculated, by a combination of each of the rotation angle detection signals to be output from such the encoder and the magnetic sensor individually.
[Patent Document 1] Japanese Patent Application Publication No. 2001-505667
[Patent Document 2] Japanese Patent Application Publication No. 2002-098522